Question

What is the key difference between lanthanoid contraction and actinoid contraction?

Answer 1

The difference between lanthanoid contraction and actinoid contraction is as follows:

Lanthanoid contraction	Actinoid contraction
The atomic size or the ionic radii of tri-positive lanthanide ions decrease steadily from Cerium $\mathrm{Ce}$ to Lutetium $\mathrm{Lu}$ due to increasing nuclear charge and electrons entering the inner (n-2) f orbital. This gradual decrease in the size with an increasing atomic number is called lanthanide contraction.	The atomic size or the ionic radii of tri positive actinides ions decrease steadily from Thorium $\mathrm{Th}$ to Lawrencium $\mathrm{Lw}$ due to increasing nuclear charge and electrons entering the inner (n-2) f orbital. This gradual decrease in the size with an increasing atomic number is called actinide contraction.
The size contraction is smaller in lanthanoids.	The size contraction is more in actinoids.
It involves the filling of the $4\mathrm{f}$ orbital.	It involves the filling of the $5\mathrm{f}$ orbital.